/* -*- P4_16 -*- */
#include <core.p4>
#include <v1model.p4>

const bit<16> TYPE_IPV4 = 0x800;
const bit<16> TYPE_SRCROUTING = 0x1234;

#define MAX_HOPS 9

/*************************************************************************
*********************** H E A D E R S  ***********************************
*************************************************************************/

typedef bit<9>  egressSpec_t;
typedef bit<48> macAddr_t;
typedef bit<32> ip4Addr_t;

header ethernet_t {
    macAddr_t dstAddr;
    macAddr_t srcAddr;
    bit<16>   etherType;
}

header srcRoute_t {
    bit<1>    bos;
    bit<15>   port;
}

header ipv4_t {
    bit<4>    version;
    bit<4>    ihl;
    bit<8>    diffserv;
    bit<16>   totalLen;
    bit<16>   identification;
    bit<3>    flags;
    bit<13>   fragOffset;
    bit<8>    ttl;
    bit<8>    protocol;
    bit<16>   hdrChecksum;
    ip4Addr_t srcAddr;
    ip4Addr_t dstAddr;
}

struct metadata {
    bit<3>    packet_type; // 0: unknown, 1: IPv4, 2: Source Routing
}

struct headers {
    ethernet_t              ethernet;
    srcRoute_t[MAX_HOPS]    srcRoutes;
    ipv4_t                  ipv4;
}

/*************************************************************************
*********************** P A R S E R  ***********************************
*************************************************************************/

parser MyParser(packet_in packet,
                out headers hdr,
                inout metadata meta,
                inout standard_metadata_t standard_metadata) {

    state start {
        transition parse_ethernet;
    }

    state parse_ethernet {
        packet.extract(hdr.ethernet);
        transition select(hdr.ethernet.etherType) {
            TYPE_SRCROUTING: parse_srcRouting;
            TYPE_IPV4: parse_ipv4;
            default: accept;
        }
    }

    state parse_srcRouting {
        packet.extract(hdr.srcRoutes.next);
        meta.packet_type = 2; // Source Routing packet
        transition select(hdr.srcRoutes.last.bos) {
            0: parse_srcRouting;
            1: parse_ipv4;
        }
    }

    state parse_ipv4 {
        packet.extract(hdr.ipv4);
        // If we reach here from Ethernet parsing, it's IPv4 packet
        if (meta.packet_type == 0) {
            meta.packet_type = 1; // IPv4 packet
        }
        transition accept;
    }
}

/*************************************************************************
************   C H E C K S U M    V E R I F I C A T I O N   *************
*************************************************************************/

control MyVerifyChecksum(inout headers hdr, inout metadata meta) {
    apply {  }
}

/*************************************************************************
**************  I N G R E S S   P R O C E S S I N G   *******************
*************************************************************************/

control MyIngress(inout headers hdr,
                  inout metadata meta,
                  inout standard_metadata_t standard_metadata) {

    action drop() {
        mark_to_drop(standard_metadata);
    }

    // Source Routing action
    action srcRoute_nhop() {
        // Set egress port from source route stack
        standard_metadata.egress_spec = (egressSpec_t) hdr.srcRoutes[0].port;

        // Remove top entry by shifting the stack
        hdr.srcRoutes[0] = hdr.srcRoutes[1];
        hdr.srcRoutes[1] = hdr.srcRoutes[2];
        hdr.srcRoutes[2] = hdr.srcRoutes[3];
        hdr.srcRoutes[3] = hdr.srcRoutes[4];
        hdr.srcRoutes[4] = hdr.srcRoutes[5];
        hdr.srcRoutes[5] = hdr.srcRoutes[6];
        hdr.srcRoutes[6] = hdr.srcRoutes[7];
        hdr.srcRoutes[7] = hdr.srcRoutes[8];
        hdr.srcRoutes[8].setInvalid();
    }

    action srcRoute_finish() {
        hdr.ethernet.etherType = TYPE_IPV4;
    }

    // IPv4 Forwarding action
    action ipv4_forward(macAddr_t dstAddr, egressSpec_t port) {
        standard_metadata.egress_spec = port;
        hdr.ethernet.srcAddr = hdr.ethernet.dstAddr;
        hdr.ethernet.dstAddr = dstAddr;
    }

    action update_ttl(){
        hdr.ipv4.ttl = hdr.ipv4.ttl - 1;
    }

    // IPv4 forwarding table
    table ipv4_lpm {
        key = {
            hdr.ipv4.dstAddr: lpm;
        }
        actions = {
            ipv4_forward;
            drop;
        }
        size = 1024;
        default_action = drop;
    }

    apply {
        if (hdr.ethernet.isValid()) {
            // Handle Source Routing packets
            if (hdr.ethernet.etherType == TYPE_SRCROUTING && hdr.srcRoutes[0].isValid()) {
                if (hdr.srcRoutes[0].bos == 1) {
                    srcRoute_finish();
                }
                srcRoute_nhop();
                if (hdr.ipv4.isValid()) {
                    update_ttl();
                }
            }
            // Handle IPv4 packets
            else if (hdr.ethernet.etherType == TYPE_IPV4 && hdr.ipv4.isValid()) {
                ipv4_lpm.apply();
                if (standard_metadata.egress_spec != 0) {
                    update_ttl();
                }
            }
            else {
                drop();
            }
        } else {
            drop();
        }
    }
}

/*************************************************************************
****************  E G R E S S   P R O C E S S I N G   *******************
*************************************************************************/

control MyEgress(inout headers hdr,
                 inout metadata meta,
                 inout standard_metadata_t standard_metadata) {
    apply {  }
}

/*************************************************************************
*************   C H E C K S U M    C O M P U T A T I O N   **************
*************************************************************************/

control MyComputeChecksum(inout headers hdr, inout metadata meta) {
    apply {  }
}

/*************************************************************************
***********************  D E P A R S E R  *******************************
*************************************************************************/

control MyDeparser(packet_out packet, in headers hdr) {
    apply {
        packet.emit(hdr.ethernet);
        // Always emit source routes if they exist - the switch will handle validity
        packet.emit(hdr.srcRoutes);
        packet.emit(hdr.ipv4);
    }
}

/*************************************************************************
***********************  S W I T C H  *******************************
*************************************************************************/

V1Switch(
MyParser(),
MyVerifyChecksum(),
MyIngress(),
MyEgress(),
MyComputeChecksum(),
MyDeparser()
) main;
